Patent Literature 1 discloses a throttle device which increases and decreases an opening degree of an intake passage of an internal-combustion engine, and the intake passage is opened slightly while operation of the internal-combustion engine is stopped. That is, the intake passage is maintained to have the minute opening degree while the operation of the internal-combustion engine is stopped, and the minute opening degree is hereafter referred to a default opening degree.
The throttle device of Patent Literature 1 includes a valve object, an electromotive actuator, and a torsion coil spring. The valve object is rotatably housed in an intake passage, and increases and decreases the opening degree of the intake passage. The actuator has an electric motor and a reduction gear. Torque produced by the electric motor is increased by the reduction gear, and is transmitted to the valve object, such that the valve object can be rotated on both sides to open and close. The coil spring has a return spring and a default spring. The return spring mainly biases the valve object to a closing side during operation of an internal-combustion engine, and the default spring mainly biases the valve object to an opening side while the operation of the internal-combustion engine is stopped.
A throttle device having a default opening degree is known, in which one torsion spring integrally has a return spring and a default spring to reduce the number of the components (refer to Patent Literature 2).
In Patent Literature 2, two torsion coil springs respectively functioning as a return spring and a default spring are connected with each other so that the torsion directions are opposite from each other. Moreover, a middle hook having U-shape is disposed between the two coil springs, e.g., a coil spring called as one side spring arranged at one side in the axial direction, and a coil spring called as the other side spring arranged at the other side in the axial direction. The axial direction means a direction of the axis of the torsion spring.
When the one side spring functions as the return spring, and when the other side spring functions as the default spring, one end of the one side spring in the axial direction is hooked on a locking part defined in, for example, a housing to be fixed, and the other end of the other side spring in the axial direction is hooked on a rotor rotated by an actuator to be rotatable. The middle hook is rotatable or fixed depending on the rotation angle of a valve object. Specifically, the middle hook is rotatable when the rotation angle is on the opening side of a rotation angle corresponding to a default opening degree, and the middle hook is fixed when the rotation angle is on the closing side of the rotation angle corresponding to the default opening degree.
When the rotation angle of the valve object is on the opening side than the rotation angle corresponding to the default opening degree, the middle hook is rotatable by being hooked by an engaging piece defined in the rotor. When the rotation angle of the valve object is on the closing side than the rotation angle corresponding to the default opening degree, the middle hook is fixed by the locking part of the housing.
In the coil spring of Patent Literature 2, the middle hook functions as a torque change part where the torque changes. However, a portion near the middle hook may be affected in the orientation when attaching the torsion spring to a throttle device. For this reason, a clearance between coil turns may become narrow at the location near the middle hook, and a contact may occur between the coil turns adjacent to each other in the axial direction.